Polyfluoroalkanoic compounds and their preparation



Patented July 10, 1951 LUNlTED STATES PATENT OFFICE POLYFLUOROALKANOIC COMPOUNDS AND THEIR PREPARATION Kenneth L. Berry, Hockessin, DcL, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application December 13, 1948, Serial No. 65,065

13 Claims. 1

This invention relates to a new class of fluerinated organic compounds. More particularly, this invention relates to certain'new fluorocarboxylic acids, to their salts and to methods for their preparation.

In spite of the great technical interest of fiuorinated organic compounds and of the considerable advances made in their chemistry in the last few years, long chain fiuorocarboxylic acids of high fluorine content have heretofore remained unknown. The synthesis of aliphatic fluorocarboxylic acids is notoriously difficult and there are no known general or even specific methods of preparing those acids having seven or more carbon atoms.

It is an object of this invention to provide'new polyfluoroalkanoic acids and their salts. A further object is to provide new methods of preparing polyfluoroalkanoic acids and their salts. A still further object is to provide new polyfiuoroalkanoic acids which have extreme stability and inertness. Another object is to provide new polyfluoroalkanoic acid salts which have marked surface-active properties. Still another object is to provide new polyfluoroalkanoic acids and their salts which have many novel and useful properties. Other objects will appear hereinafter.

These and other'objects and advantages are accomplished by providing a new class of chemical compounds, the polyfiuoroalkanoic compounds consisting of the straight chain polyfiuoroalkanoic acids and their inorganic salts of the formula H CX2CX2)11COOM, wherein X is a halogen of atomic weight below 40, that is fluorine or chlorine, and at least half of the Xs are fluorine, n is an integer from 3 to inclusive and M is hydrogen, or an ammonium or metal cation. These new polyfluoroalkanoic acids have the formula H(CX2CX2) nCOOH, wherein the X substituents are halogen atoms of atomic weight below 40 and at least half of the halogen atoms in each CXzCXz group are fluorine and n is a positive integer from 3 to 10 inclusive. The preferred new polyfluoroalkanoic compounds have the formula H(CF2CF2)1;COOM, wherein n is a positive integer from 3 to 10 inclusive and M is defined as aforesaid. The preferred straight chain polyfiuoroalkanoic acids have the formula H(CFzCF2)1.COOH, wherein n is a positive integer from 3 to 10 inclusive.

This invention also provides a method of preparing these new polyfluoroalkanoic acids and their salts which comprises permanganate oxidation of a polyfiuoroalkanol which is the reaction product of methanol and a fully halogenated polyfiuoroethylene, said polyiluoroalkanol having the formula H(CX2CX2)1LCH2OH, wherein X is a halogen of atomic weight below 40 and at least half of the Xs in each CX2CX2' group are fluorine and n is an integer'from 3 to 10 inclusive. The

preferred polyfiuoroalkanols are the reaction products of methanol and tetrafluoroethylene and have the formula H CF2CF2 nCHZOH, wherein n is a positive integer from 3 to 10 inclusive.

In the preferred mode of operating the process of this invention, the polyfluoroalkanol to be oxidized is dissolved in a suitable organic acid, such as the alkanoic acids, for example, acetic acid. The solution is brought to a temperature between 50 and 100 C. and treatedportion-wise with finely ground potassium permanganate, pref erably used in excess. The resulting polyfluoroalkanoic acid may be isolated by various means. To obtain it in a pure state on a small or moderate scale, it is desirably isolated as the crude manganous salt, from which the free acid is obtained by acidification followed by distillation and/or crystallization.

The starting materials, 1. e., the polyfluoroalkanols of the general formula wherein the Xs represent halogen atoms of atomic weight below 40, at least half of which in each CXzCXz group are fluorine, and n is an integer from 3 to 10 inclusive, may be prepared by the method described in copending application Serial No. 65,063, filed by R. M. Joyce on December 13, 1948, as a continuation-in-part of application Serial No. 567,777, filed December 11, 1944, and now abandoned. This method consists in heating at a suitable temperature, such as between and 350 C., in thepresence of a free radical-producing catalyst, a mixture of methanol with a completely halogenated fiuoroethylene containing at least two fluorine atoms, the remaining halogen atoms, if any, being chlorine atoms. Preferably, the fiuoroethylene compound is tetrafiuoroethylene. The catalyst may be, for example, an organic or inorganic peroxide such as diethyl peroxide, di-tert. butyl peroxide, benzoyl peroxide, lauroyl peroxide, hydrogen perox ide, and the like; or it may be one of the very active catalysts described in application Serial No. 2,551, filed by Madison Hunt on January 15, 1948, now Patent No. 2,471,959, i. e., an organic azo compound wherein the azo, -N=N, group is acylic and bonded from both its nitrogen at:- oms to aliphatic carbon atoms, at least one of which is tertiary, particularly the azobis(alphaa 3 cyanoalkanes) such as a.lpha,alpha'-azodiisobutyronitrilej alpha,alpha' azobisialpha, gammadimethylvaleronitrile); 1,1 azodicyclohexanecarbonitrile, and the like; or it may be a salt of a peracid, such as ammonium per-sulfate, sodium perborate. potassium percarbonate and the like.

The products of 'this reaction, as carried out for example between tetrafluoroethylene and methanol, are mixtures of polyfluoroalkanols of the formula H(CF2CF2) nCHZOH. These mixtures may be separated, e. g. by steam distillation, fractional distillation and/or fractional crystallization from appropriate solvents, into rather well defined constituents wherein n has various values between the limits stated. While tetrafiuoroethylene is the preferred reagent, other com pletely halogenated ethylenes containing chlorine may be used, these compounds including chloro trifluoroethylene, 1,1-dichloro 2,2 difluoroethylene and 1,2-dichloro-1,2-difiuoroethylene.

For the purpose of illustrating the present invention more fully, a typical preparation of the intermediate polyfiuoroalkanols is described below.

A mixture of .150 parts of methanol and 2 parts of tert.-butyl octyle peroxide was placed in a high pressure reactor. The reactor was closed, evacuated, cooled and charged with 110 parts of tetrafluoroethylene through a valve. The reactor was agitated and heated at 170 C. for 10 hours under autogenous pressure (90 atm.) The reaction product was subjected to steam distillation. The steam-volatile material was a mixture of liquid and solid product which was separated into the two phases. The liquid raction was subjected to fractional distillation, giving a series of compounds H(CF2CF2)1;CH2OH. The solid steamvolatile fraction was recrystallized from chloroform to give 17.5 parts of the compound, in which 1:. equals 6 and a second fraction, parts, in which n equals 5. The filtrate from the recrystallization was evaporated and distilled to give 18 parts of a mixture of the compounds in which n equals 4 and 5. Longer chain polyfluoroalkanols may be isolated by fractional crystallization or sublimation. For example, fractional sublimation of the non steam-volatile fraction gives polyfiuoroalkanols in which n is 6, '7 and 8. The properties of some of these materials are shown .in the table below.

tm rlcrmomou The oxidizing agent used for the conversion of the 'polyfiuoroalkanols to the corresponding acids is an alkali or alkaline earth metal permanganate, which is preferably potassium permanganate but can also be, for example, sodium, lithium, calcium or barium permanganate. It has been found that the permanganates are specific oxidizing agents in the process of this invention. However, the combination of nitric acid with nitrogen peroxide (N204) will also efiect the oxidation under sufliciently drastic conditions. Other conventional oxidizing agents, such as perchloric acid, chromic oxide, sodium hypochlorite or Ill hydrogen peroxide are ineffective. The oxidation is preferably carried out in acidic media, although alkaline oxidation can also be used. The best results are obtained when the polyfiuoroalkanol is dissolved in a saturated carboxylic acid such as acetic, propionic, or butyric acid, which solution may contain other solvents or diluents such as water. acid such as sulfuric acid may be used as the reaction medium but the oxidation is then slower than when the polyfiuoroalkanol is in solution. The permanganate is preferably added portionwise, as a finely divided solid or as an aqueous or acetic acid solution, until its purple color is no longer discharged at an appreciable rate. The reaction temperature is not critical and any desired temperature between 0 C. and the boiling point of the solution may be used. A preferred range is between 50 and C.

The resulting polyfiuorocarboxylic acid is most conveniently isolated from the oxidation mixture as the crude manganous salt by evaporation of the solvent or diluent. Upon acidification of the salt, the free acid is formed and can be obtained by solvent extraction and distillation. If desired, the manganous salt may be purified, prior to acidification, by dissolving it in an appropriate solvent and reprecipitating it therefrom. The manganous salt may also be converted to an alkali metal salt, e. g., the sodium or potassium salt, and the latter may be acidified to isolate the free acid.

The invention is illustrated in greater detail in the following examples, in which parts are by weight. 7

Example I A solution of 66 parts of dodecafluoro-l-heptanol, H(CF2.CF2)3CH2OH, in 200partsof glacial acetic acid was treated at 70-100 C. with 42 parts of finely divided potassium permanganate added gradually. The manganese dioxide which had formed was reduced by bubbling sulfur dioxide into the solution until the dark color was discharged. The acetic acid was distilled from the mixture under reduced pressure and finally removed by codistillation with toluene. The crude manganese salt of dodecafluoroheptanoic acid (71 parts) was dissolved in dilute sulfuric acid and the solution was extracted with ether. Distillation of the ether solution gave 29- parts of free acid, B. P. -193 0., neutral equivalent 332. The acid was converted to the potassium salt by addition of 12 parts of potassium hydroxide to an ethanol solution of the acid. The potassium salt of dodecafluoroheptanoic acid was precipitated from the filtrate by addition of toluene and boiling. There was thus obtained 25 parts of pure potassium dodecafluoroheptanoate. This was a white crystalline solid highly soluble in water and appreciably soluble in a number of organic solvents such as ethanol, methanol, acetic acid and phenol. A 0.2% aqueous solution of potassium dodecafluoroheptanoate had a surface tension of 50.8 dynes/cm. at 25 C., as compared to 71.7 for pure water. The free acid was also prepared by dissolving the potassium salt in dilute sulfuric acid and extracting with ether. The ether solution was distilled, leaving the free dodecafiuoroheptanoic acid, B. P. 192 C.

Example II A. solution of 69 parts of hexadecafluorononanol, H(QF2CF2)4CH2OH, in 500 parts of glacial acetic acid was treated at 70-100 C. with 59 parts of finely ground potassium permanganate and re- Water alone, as such or containing an ample I, thenredissolved in 1000 parts of ethanol and converted'toithe potassium salt by addition of potassium hydroxide is the boilin'g'fethanolsm lution. The precipitated manganese dioxide was filtered from the solution. and by the of Example I there was-obtained 52 parts oflcrude potassium hexadecafiuorononano'at'ei The acid was isolated by acidifying the salt with dilute sulfuric acid, extracting with ether, evaporating the ether and recrystallizing the residue from ben-v zene. The acid had a melting pointof 62-68 C.,

a boiling point of 220-230 C. and a neutralization equivalent of 463 (calculated: 446). The potassium salt was soluble in water and appreciably soluble in organic solvents such as ethanol. methanol, acetic acid and phenol. A 0.2% aqueous solution of this salt had a surface tension of 35.6 dynes/cm. at 25 C., as compared to 71.7 for pure water.

Example III A solution of 2'7 parts of eicosafluoroundecanol, H(CF2CF2) 5CH2OH (M. P. 95-97 C.) in 500 parts of glacial acetic acid was treated at 100 C. with 32 parts of finely ground potassium permanganate. The manganese dioxide formed in the reaction was reduced by bubbling sulfur dioxide into the reaction mixture until the dark color was removed.

The acetic acid was removed b distillation under reduced pressure and the last traces were removed by codistillation with toluene. The solid residue was then extracted several times with water and the insoluble manganese salt of eicosafiuoroundecanoic acid was filtered, dissolved in ethanol and converted to the potassium salt by treatment with excess potassium hydroxide. Upon boiling the solution, manganese dioxide precipitated and was removed by filtration. The potassium salt was then precipitated from the alcohol filtrate by treatment with toluene at the boiling point. Crystallization of the crude salt from an ethanol-toluene mixture give parts of pure potassium eicosafluc-roundecanoate. This was a solid soluble in water and whose 0.2% aqueous solution had a surface tension of 34.6 dynes/cm. The free eicosafluoroundecanoic acid was obtained by dissolving the potassium salt in dilute sulfuric acid and extracting the resulting slurry with ether. Alternatively, since the acid is sparingly soluble in water it may be filtered from the acidic aqueous solution and purified by crystallization from toluene. Eicosafiuoroundecanoic acid is a crystalline solid melting at 100-101 C., sparingly water-soluble and soluble in benzene, toluene,

chloroform, carbon tetrachloride, ether, methanol and ethanol. Its neutralization equivalent was 564 (calculated: 546).

Example IV A solution of 21 parts of tetracosafiuorotridecanol, H(CF2CF2) sCHzOH, in 300 parts of glacial acetic acid was treated gradually at 100 C. with parts of finely ground potassium permanganate, then refluxed for 1 hour. The manganese salt of tetracosafiuorotridecanoic acid was isolated as in the preceding examples, then treated directly with dilute sulfuric acid and the acidified mixture was extracted with ether. The ether solution was evaporated and the residue was crystallized from benzene, giving 8 parts of tetracosafluorotridecanoic acid, M. P. 138 C., neutralization equivalent 642 (calculated: 646) A 0.2% aqueous solution of potassium tetracosafluorotrldeeanoatc has a surface tension of 38.6 dimes/cm. at25'C. m. lZ.

Twenty-fiveparts of amixture of polyfluoroalkancls H(CECE= nCHiOH consisting chiefly of finine, eleven and thirteen carbon compounds, with some hi hgr fractions, was dissolved in 100 parts "oi' glacial acetic acid. This solutionwas *andmaintainedat 50-6? C. of

15 of powdered to in; small increments over a of 3 hours. The j reaction was finally'refiuxed for 10 min- 'utas, 'cooleddililted with water, and filtered. The filter cake of dioxide was washed with hot glacial acetic-acid. .Thefiltrate was evaporated leaving a residue .ofthe reactionpmduct in the form of crude'saltsi in 500 parts of boiling water which was then strongly acidified with hydrochloric acid.-j..$even parts of a reddish brown ofl separated aml upon cooling. Three parts of this crude acid was dissolved in 50 parts of boiling carbon tetrachloride, which solution was filtered and cooled. The crystalline polyfluomalkanoic acid mixture which separated had a melting point in the range of 77438 C. and a neutralization equivalent of 684, indicating that the average of the composition was H(CF1) 12.1COOH.

Example VI Five parls of a mixture of polyfluonopolychlr gralkanols boiling at 110-130 C. at 4 mm. pressure (obtained by heating under autogennus pressure methanol and trifluorochloroetlrylene with alpha, alpha'azod.iisobutyronitrile catalyst at '10" C. for 8 hours) was disolved in 50 parts of glacial acetic acid and the solution was treated slowly at the boiling point with 10 parts of potassium permanganate. Afte the addition was complete and the resulting sludge had been refluxed several minutes, sulfur dioxide was bubbled into the reaction mixture until it became clear. The solution was evaporated to dryness at 2 mm. pressure and the residue was washed with 20 parts of toluene, then treated with water and acidified with sulfuric acid. There was formed a two-layer solution which was extracted with two 20-part portions of ether. The combined ether extracts, after drying and removing the ether, gave on distillation 1 part of a clear liquid boiling at 42 C. at 45 mm. pressure and 0.5 part of a yellow oil boiling at 100-130 C. at 3 mm. pressure. The first fraction had a neutralization equivalent of 145.7, indicating that it was chiefly the acid H(CT3C1)C0OH, probably mixed with a little acetic acid. The second fraction had a neutralization equivalent of 414.7, corresponding to the acid H CzF3Ci) 3000B. (calculated neutralization equivalent: 395.5) mixed with a little of the acid H(C2F:Cl) 4000B.

Emmple VI! A mixture of 2.5 parts of hexadecafluorononanol H(CF&CF&)4CH:OH, with 12.5 parts of aqueous nitric acid was cooled in an ice water bath and there was added 3 parts of liquid nitrogen peroxide, N204. This mixture was placed in anopen glasstubeenclosedinastainlesssteel autoclave having a capacity of approximately parts water- The autoclave was then sealed and immersed in a bath of heat transfer salt heated at 280 C. A presure of I00 lb./sq. in. was reached in about 15 minutes and these reaction conditions were maintained for Kr hour. The autoclave was then removed from the both.

dissolved in parts of water.

, fluorinated greases.

cooled, and the pressure released. The contents of the glass tube separated into 2 layers. The lower organic layer was separated from the upper aqueous layer and dissolved in 20% aqueous so- .dium hydroxide. Hexadecafluorononanol was re moved by filtration. The filtrate was then acidified with hydrochloric acid to obtain hexadecafluorononanoic acid.

The products of this invention are the straight copper, calcium, zinc, barium, mercury, aluminum, manganese, iron salts, etc. For example, an aluminum polyfluorocarboxylate which has special uses as an ingredient of greases may be prepared as follows:

Six parts of the potassium salt of a mixture of polyfluorocarboxylic acids having the average composiion H(CF2)12COOH was placed in 600 parts of boiling water and to this solution was added 1.5 parts of aluminum sulfate,

Alz(SO4) 3.181120 A gelatinous preciptate of aluminum polyfluorocarboxylate separated. This was filtered and dried, dissolved in about 50 parts of acetone and the solu .ion was filtered. The salt was reprecipitated from the acetone filtrate by treatment with about 200 parts of water. The mixure was boiled to remove the acetone and there was isolated, by filtration and drying, 4.5 parts of the purified aluminum polyfiuorocarboxylate.

The most useful compounds obtainable by this invention are the fluorinated acids and salts of the formula H(CF2CF2)11CO0M wherein n is an integer from 4 to 8 and M is hydrogen or an ammonium or metal cation, since these specific compounds have been found most effective in the technical applications outlined below.

The polyfluoroalkanoic acids of this invention are highly stable, nonfiammable materials useful as chemical intermediates, e. g. in the synthesis or highly fiuorinated esters, amides, etc. Their ammonium and alkali metal salts exhibit marked surface-active properties (evidenced only for those acids having at least 7 carbon atoms) which makes them useful as wetting, dispersing and emulsifying agents havin high stability. For example, the ammonium and alkali metal salts are valuable dispersing agents in the aqueous polymerization of various polymerizable materials. Specifically, it is possible with their use to polymerize tetraflu'oroethylene in aqueous systems directly to colloidal polymer dispersions having very high solids contents, an operation which is not possible with, the conventional emulsifying agents. Among the other metallic salts of polyfluoroalkanoic acids, the aluminum salts are especially useful as ingredients of For example, by dissolving an aluminum polyfluorocarboxylate in a perfiuorinated hydrocarbon and cooling the solution, a high melting, heat-reversible gel is obtained. Such gels have high film strength with good friction-reducing properties, are nonbleeding and non-flammable and have good adhesiveness. They are therefore attractive as lubricants in severe environments where resistance to heat, chemicals, solvents and/or oxidation is desired. The preparation of a grease of this type is described below.

Three parts of a perfiuorinatedoil, B. P. 190 C. at 10 mm. pressure, which had been prepared by the substantially complete fluorination in the vapor phase of lubricating oil with cobalt trifluoride, was mixed with one part of the aluminum salt of a mixture of polyfiuorocarboxylic acids having the average composition H(CF2)icCOOH. The mixture was heated for several minutes at about 200 0. to obtain a clear, homogeneous solution. This solution was allowed to cool. At 180 C. it solidified to a firm, heat-reversible gel which did not synerize or bleed upon further cooling to room temperature and storing at this or any temperature up to the gel melting point. This gel was a firm grease with good adhesion to glass and metal surfaces and which had good film strength and lubricating properties on glass or metal valves. Another composition comprising 5.7 parts of perfluorinated oil and 1 part of aluminum polytluorocarboxylate had similar properties. A 5% solution of the same aluminum salt in a per-.

fiuorinated oil boiling at 210-240 C. at 10 mm. pressure was a non-gelling, clear, sticky lubricating composition.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A polyfluoroalkanoic compound having the formula H(CX2CX2)COOM wherein the X substituents are'halogen atoms of atomic weight below '40 and at least half of the halogen atoms in each CXzCX-z group are fluorine, n is a positive. interger from 3 to 10 inclusive and M is a member of the class consisting of hydrogen, ammonium and metal cations.

2. A polyfluoroalkanoic compound having the formula H(CF2CF2)1;COOM wherein n is a positive integer from 3 to 10 inclusive and M is a member of the class consisting of hydrogen, ammonium and metal cations.

3. A polyfiuoroalkanoic acid having the formula H CX2C&)COOH wherein the X substituents are halogen atoms of atomic weight below 40 and at least'half of the halogen atoms in each CXzCXz group are fluorine, and n is a positive integer from 3 to 10 inclusive.

4. A polyfluoroalkanoic acid having the formula H(CFzCF2)nCOOI-I wherein n is a positive interger from 3 to 10 inclusive.

5. A method for preparing polyfluoroalkanoic compounds which comprises oxidizing a polyfiuoroalkenol with a member of the class consisting of the alkali and alkaline earth metal permanganates, said polyfiuoroalkanol having the formula H(CX2CX2) nCH2OH wherein the X substituents are halogen atoms of atomic weight below 40 and at least half of said halogen atoms in each CXzCXz group are fluorine. and n is a. positive integer from 3 to 10 inclusive.

6. A method for preparing polyfluoroalkanoic compounds which comprises oxidizing a polyfluoroalkanol with a member or the class consisting of the alkali and alkaline earth metal permanganates, said poiyfluoroalkanol having the formula H(CF2CF=)CH:OH wherein n is .a positive integer from 3 to 10 inclusive.

7. The method et forth in-claim 6 in which said polyfluoroalkanol is oxidized in an alkanoic acid solvent. a

8. The method set form in claim 6 in which said polyfluoroalkanol is oxidized with potassium permanganate.

9. A method for preparing polyfluoroalkanoic acids which comprises oxidizing a polyfiuoroalkanol dissolved in acetic acid with potassium permanganate, said polyfluoroalkanol having the formula mcmcnhsmorr wherein n is a positive integer from 3 to 10 inclusive.

10. A mixture of polyfluoroalkanoic acids having the formula H(CF:CF:).;COOH wherein n is a positive integer from 4 to 8.

11. The polyfluoroalkanoic acid, hexadecafluorononanoic acid havin the formula Number 13. The polvfluoroalkanoic acid, tetracosafiucrotridecanoic acid having the formula H(CF2CF2)0COOH KENNETH L. BERRY.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Countrv Date Great Britain Aug. 25, 1936 OTHER REFERENCES Henne et al.. Am. Chem soc vol. 67, pp. 918

and 919.

Bulletins de LAcademie Royale de Belgique- Ciasse de Sciences (1902) p. 757, 

1. A POLYFLUOROALKANIC COMPOUND HAVING THE FORMULA H(CX2CX2)NCOOM WHEREIN THE X SUBSTITUENTS ARE HALOGEN ATOMS OF ATOMIC WEIGHT BELOW 40 AND AT LEAST HALF OF THE HALOGEN ATOMS IN EACH CX2CX2 GROUP ARE FLUORINE, N IS A POSITIVE INTERGER FROM 3 TO 10 INCLUSIVE AND M IS A MEMBER OF THE CLASS CONSISTING OF HYDROGEN, AMMONIUM AND METAL CATIONS. 